Untag passing Time.at specs

Author: andrykonchin

spec/tags/core/time/at_tags.txt

@@ -1,4 +1,2 @@
-fails:Time.at passed Numeric roundtrips a Rational produced by #to_r
 fails:Time.at :in keyword argument could be a timezone object
 fails:Time.at passed non-Time, non-Numeric with an argument that responds to #to_r needs for the argument to respond to #to_int too
-fails:Time.at :in keyword argument raises ArgumentError if format is invalid